This invention relates to methods for determining the efficacy of decontamination procedures, and more particularly, to a method for testing the efficacy of decontamination procedures for endoscopes and other lumened surgical instruments.
Prior to placing any surgical instrument within a patient, the instrument should be decontaminated (i.e., cleaned, disinfected, sterilized and/or water-rinsed) to avoid infecting the patient with contaminants or microorganisms on the instrument. Decontamination is especially challenging for lumened instruments, such a flexible endoscopes, which are repeatedly contaminated and decontaminated. Endoscopes are particularly difficult to decontaminate due to their design, which includes a variety of internal channels that are difficult to clean and access.
Medical professionals have an ever-increasing variety of decontamination methods from which to select. Selecting an effective decontamination method would be easier if an evaluation method existed to determine the efficacy of different decontamination methods. Medical professionals could use such an evaluation method to verify and document that they adequately decontaminated their instruments prior to surgery.
Users and suppliers of decontamination equipment and accessories (e.g., detergents and sterilants) would also be aided by a method for determining the efficacy of different decontamination methods.
Surgical instrument manufacturers (e.g., flexible and rigid endoscope manufacturers) would also be aided by a method for determining the efficacy of different decontamination methods. These manufacturers potentially could show that their instruments can be effectively decontaminated, and could specify that the end user employ a specific decontamination method that has been verified as adequate (i.e., validated).
All references cited herein are incorporated herein by reference in their entireties.
A method determines the efficacy of a decontamination procedure. The method includes providing a test object and a control object. The test object is contaminated with a first known amount of inoculum that includes microorganisms. The control object is contaminated with a second known amount of the inoculum. The first known amount of inoculum and the second known amount of inoculum is substantially the same. The decontamination procedure is performed on the contaminated test object but not on the contaminated control object. The microorganisms from the decontaminated test object and the contaminated control object are recovered. A number of microorganisms recovered from the decontaminated test object is compared with a number of microorganisms recovered from the contaminated control object. The decontamination procedure is deemed effective when the number of microorganisms recovered from the decontaminated test object is at least 3 logs less than the number of microorganisms recovered from the contaminated control object.
Another embodiment of the method includes performing a first sampling technique on the decontaminated test object and a second sampling technique on the contaminated control object. The first sampling technique and the second sampling technique are the same and are operative to recover the microorganisms from respective ones of the decontaminated test object and the contaminated control object. The decontamination procedure is deemed effective relative to the sampling technique when the number of microorganisms recovered from the decontaminated test object is at least 3 logs less than the number of microorganisms recovered from the contaminated control object.
Conventional methods for evaluating the efficacy of a decontamination process that do not use control instruments can yield erroneous results. For example, a known amount of an inoculum of viable microorganisms is applied onto internal surfaces forming internal lumens of a test instrument. This instrument is decontaminated using a prescribed decontamination process. Typically, a sterile fluid is used for sampling the lumens. Usually, the sterile fluid is rinsed through one end of the lumen, collected aseptically at the opposite end of the lumen and then analyzed microbiologically.
The efficacy of the decontamination process is assessed by measuring and comparing the number of microorganisms recovered from fluid rinsed through the test instrument to the known number of microorganisms originally applied to the test instrument. The lower the number of recovered microorganisms, the more efficacious the process is presumed to be. If the fluid is found to be sterile, the lumen is assumed to be sterile due presumptively to the prescribed decontamination process having destroyed all of the microorganisms inoculated onto the lumen surfaces.
This conclusion might be erroneous, however. It cannot be assumed that because the rinsing fluid was sterile, the decontamination process must have destroyed all of the microorganisms. In order for this decontamination process to be valid, the sampling technique must recover every viable microorganism on the lumen surfaces after exposure to the decontamination process. The rinse sampling technique might be invalid because microorganisms that survive the decontamination process may adhere to the lumen surfaces and not be recovered during the rinse sampling technique. Thus, due to the limitations of the rinse sampling technique, the decontamination process may be presumed to have destroyed all of the microorganisms on the lumen surfaces when, in fact, some microorganisms may have survived but cannot be recovered by the sampling technique. The method uses a control object to remove this potential artifact from being introduced into the data.
Bioburden: The number and type of viable microorganisms used to contaminate instruments.
CFU: Colony Forming Units.
CFU/ml: A concentration of microorganisms, expressed as colony forming units per unit milliliter of volume.
Cleaning: The removal of foreign materials, such as organic soil (e.g., protein and/or blood serum) and microorganisms, from an object such as, e.g., a medical instrument.
High-level Disinfection: The complete destruction and/or removal of all microbal life, except for high numbers of bacterial endoscopes.
Sterilization: The complete destruction and/or removal of all microorganisms.
Decontamination: The process of cleaning, disinfecting, sterilizing and/or water-rinsing an object. The object can be subjected to any combination or permutation of these steps.
Detergent solution: A solution used to aid in cleaning objects:
Automated decontamination: The use of an automated device to decontaminate objects.
Starting titre: The concentration of microorganisms (expressed as CFU/ml) used to contaminate both the control and test instruments.
Manual decontamination: The decontamination of objects without the aid of an automated device.
Accessible sites: Refers to those locations on a reusable medical instrument that can be accessed and decontaminated.
Inaccessible sites: Refers to those locations on a reusable medical instrument that cannot be accessed and decontaminated.
Worst-case conditions: The intentional exaggeration of one or more parameters to create a challenge unlikely to be encountered in the clinical setting.
Reusable medical instrument: Any medical instrument that is claimed by the manufacturer to be usable after being decontaminated.
Endoscope: A generic term for a medical instrument that is used to examine hollow viscera. Examples of flexible endoscopes include broncoscopes, gastroscopes and colonoscopes. Examples of rigid endoscopes include laparoscopes and arthroscopes. Flexible endoscopes typically include internal lumens, a complex valve system, and other surfaces that need to be decontaminated after each use.
Test cycle: Exposure of an instrument to at least one of the steps of the decontamination process (e.g., cleaning, disinfecting, sterilizing and/or rinsing).
Inoculum: A volume of the starting titre (CFU) of a type (genus and species) of viable microorganisms, and organic soil used to contaminate both the control and test instruments.
Control instruments: Reusable instruments that are contaminated but not subjected to the test cycle. These instruments are used to determine the number of organisms that can be recovered.
Test instruments: Reusable instruments that are contaminated and subjected to the test cycle. These instruments are used to determine the efficacy of the decontamination process.
Control instrument recovery: The number of viable microorganisms (CFU) recovered from the control instruments.
Test instrument recovery: The number of viable microorganisms (CFU) recovered from the test instruments.
Recovery count: The control instrument recovery. This number may be significantly less than the number in the applied inoculum. (If a high-level disinfection process is being evaluated, the recovery count must be equal to or greater than 1xc3x97106 CFUs of mycobacteria. This may require the starting titre to be as high as 1xc3x97108 CFU/ml.)
Recovery efficacy: A ratio, expressed as a percentage, of the recovery count to the applied inoculum. This value is multiplied by 100 to express efficacy as a percentage. Also, a measure, in part, of the effectiveness of the sampling method used to recover microorganisms.
Cleaning efficacy: The efficacy of cleaning may be calculated as a percentage or log reduction from the recovery count to the test instrument recovery. Typically, at least a 3 log reduction (99.9%) of bioburden is required.
Cleaning effectiveness: A measure of the effectiveness of the cleaning process and can be evaluated by comparing the number of microorganisms recovered from the test instruments to the recovery count. Cleaning effectiveness can be expressed as a percent or log reduction. Typically, at least a 3 log reduction (99.9%) of a marker microorganism is required to claim cleanliness.
Disinfection efficacy: The efficacy of disinfection may be calculated as a percent or log reduction from the recovery count to the test instrument recovery. Typically, at least a 6 log reduction (99.9999%) of mycobacterium is required.
Disinfection effectiveness: A measure of the effectiveness of the disinfection process and can be evaluated by comparing the number of microorganisms recovered. from the test instruments to be recovery count. Disinfection effectiveness can be expressed as a percent or log reduction. Typically, at least a 6 log reduction (99.9999%) of mycobacterium is required to claim high level disinfection.
Sterilization efficacy: The efficacy of a sporicidal process may be calculated as a percent or log reduction from the recovery count to the test instrument recovery. Typically, at least a 6 log reduction (99.9999%) of bacterial endospores during a half-cycle (or a 12 log reduction during a full cycle) is required.
Sporicidal effectiveness: A measure of the effectiveness of the sporicidal process and can be evaluated by comparing the number of microorganisms recovered from the test instruments to the recovery count. Sporicidal effectiveness can be expressed as a percent or log reduction. Typically, at least a 6 log reduction (99.9999%) of bacterial endospores during a half-cycle (or a 12 log reduction during a full cycle, i.e., a SAL of 10xe2x88x926) is required.
Rinsing efficacy: The efficacy of a water rinsing process may be calculated by measuring the concentration (or parts per million) of chemical residues remaining on the instrument after rinsing with a copious volume of water.
Rinsing effectiveness: A measure of the effectiveness of the water rinsing process and can be evaluated by comparing the concentration (or parts per million) of chemical residues remaining on the test instruments after rinsing with water to the concentration (or parts per million) of chemical residues remaining on the control instruments.
Neutralizer: A reagent used to stop the antimicrobial activity of residual cleaning agent(s), disinfectant(s) and/or sterilant(s) that may be present on test instruments and eluted along with the target microorganisms.
British soil: Bovine serum (10 ml), saline (10 ml) and dry milk powder (6 grams).
The method of the invention can be used to evaluate the efficacy of a decontamination process for instruments, such as endoscopes, artificially contaminated with mock organic soil tagged with recoverable target microorganisms. The method determines the efficacy of the decontamination process by simulating soiling that results from actual clinical conditions.
The method can also be used to verify the claims for a multi-step decontamination process, or this method can be applied to evaluate one or more particular phases of the process, including, but not limited to, pre-cleaning, manual cleaning, automated cleaning, chemical immersion and water rinsing.
The method is particularly suitable for reusable and immersible flexible fiberoptic and video gastrointestinal endoscopes and bronchoscopes.
The method preferably uses a resistant mycobacterium species to determine high-level disinfection or a bacterial endospore species to determine sporicidal efficacy. These target organisms are used as tracers, and quantification of their removal from the object (e.g., log reduction) by the decontamination process being evaluated provides a means for determining the efficacy of the decontamination process. Worst-case conditions are preferably implemented as part of the testing method.
After at least one control and test object (and preferably at least three test objects, but maybe as many as 5), such as an endoscope, has been contaminated with an inoculum wherein only the test objects are subjected to the decontamination process to be evaluated, the efficacy of the decontamination process is assessed using standard and validated microbiologic sampling techniques, including swabbing, flushing (elution), and brushing techniques. The effectiveness of the decontamination methods can be assessed by comparing target organisms recovered from control objects (preferably at least three) substantially identical (instruments are considered to be substantially identical for present purposes if, e.g., they are the same model produced by the same manufacturer) to target organisms recovered from test objects wherein the control objects have not been subjected to the decontamination process being evaluated.
The test and control objects are contaminated identically. That is, the same sites on each are contaminated with the same amount of inoculum employing identical inoculation techniques. Preferably, more than one test object site and more than one control object site are inoculated. It is also preferred that some of the test and control sites are on external surfaces of the test and control objects and the balance of the test and control sites are on internal surfaces of the test and control objects.
The inoculum comprises microorganisms, preferably mixed with an organic soil. Preferred microorganisms include Bacillus stearothermtophilus and Mycobacterium terrae. The organic soil can be, e.g., blood serum, and/or a mock organic soil, and is preferably British soil. The concentration of the microorganisms in the inoculum should be at least 108 CFU/ml.
It is preferable to verify that the test and control object sites have been contaminated with the inoculum.
Cleaning is determined to be effective when the number of microorganisms recovered from the test object site(s) is about 3 logs less than the number of microorganisms recovered from the identical control object site(s). The mock soil is preferably tagged with microorganisms for counting.
Disinfection is determined to be effective when the number of microorganisms recovered from the test object site(s) is about 6 logs less than the number of microorganisms recovered from the identical control object site(s). The microorganisms are preferably mycobacteria.
Sterilization is determined to be effective when the number of microorganisms recovered from the test site(s) is preferably about 12 logs less than the number of microorganisms recovered from the identical control object site(s). The microorganisms are preferably bacterial endospores.
The efficacy of a decontamination procedure determined by the method of the invention can be compared with the efficacy of a different decontamination procedure also determined by the method of the invention.